Heretofor, the rotor for a rotary internal combustion engine typically has been fabricated as a single unit and has proved to be a rather complicated part. The complexity results in part from the fact that the rotor must be made hollow to accommodate a cooling medium fluid, such as oil or combustion intake charge and at the same time provide intricate shapes for purposes of structural strength, grooves for sealing elements, and combustion pockets in the triangulated outer peripheral wall of the rotor. Commercial versions of rotors have been typically formed of cast iron produced by conventional sand casting techniques. This has resulted in a raw or gross casting weight for the rotor of approximately 110 lbs. for a typical application to be used in a multi-rotor 200 horsepower engine. Unfortunately, much of this weight is trimmed as it constitutes risers, sprues, and ingate system, all being parasitic elements formed by the sand casting technique. In fact, approximately 90 lbs. is removed leaving the net casting rotor weight in the range of approximately 30 lbs. This is disadvantageous because the casting yield is very low and the cost of fabrication is high. The cost penalty is particularly severe since rotors have been formed of nodular cast iron, the preparation of which requires a nodularizing agent, such as magnesium, which deteriorates quickly after addition and the excess cast material cannot be recycled conveniently.
Some attempts by the prior art to simplify or introduce new methods of making the rotor for a rotary internal combustion engine have comprised: (a) use of powder metallurgy to make the rotor in parts, the parts being joined together to make a complete assembly, and (b) the use of drop forged parts which can be assembled to form a complete assembly such as by welding or other metal joining techniques including fasteners. The powder metallurgy technique has not been particularly successful for the reason that the various columns and ribs within the internal structure of the rotor must be made unusually thick as dictated by powder compression techniques; accordingly, the desire to reduce weight is not fully realized because of the contrary influence of increasing the internal webbing structure.
For forged parts, a draft to outer and inner walls is imparted by the forging operation; welding of the parts is restricted to the outer periphery of the mated assembly due to access; this necessitates special bisecting supporting walls for the inner periphery. This adds weight unnecessarily to the structure. Such a fabricated rotor will have a tendency to deteriorate because of high stresses on the outer peripheral wall which are not supported by a solid fabrication at the hub or inner periphery. The use of either forgings or powdered parts has not been attempted seriously for production because of the additional disadvantage that teeth must be formed on a portion of the rotor to cooperate as part of the timing mechanism for the engine; this results in undercut areas which cannot be fabricated by these techniques.